import java.util.Scanner;

public class Demo2 {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        // 注意 hasNext 和 hasNextLine 的区别
        int n = in.nextInt();

        System.out.println(func(n));
    }

    public static int func(int n ) {
        if(n <= 1) {
            return n;
        }

        return func(n-1) +func(n-2);
    }
}
